M6950DT difficult to start

[jlputnam1]

I posted a thread on the same subject/tractor about 5 weeks ago and have some additional information. The Fuel Shutoff solenoid has been replaced ($200 for this tractor - wow!) because the old one leaked fuel around the wire.

The tractor randomly will not start - no smoke or any kind of response when towed or when using the starter. The solution seems to be that the complete bleed procedure needs to be run. Two days ago the tractor started after sitting 5 weeks. The next morning it would not start until the bleed procedure was accomplished. This morning it started normally, this evening (10 hours later) it will not start. Once running, the tractor operates normally and a quick restart - within 30 minutes or less is no problem.

I've found no leaks, checked the fuel cap (looking to see that there is not a vacuum in the fuel tank), fuel quantity, fuel shutoff solenoid action (I hear the click) - no smoking gun - yet.

Still looking for ideas.

 

[Tx Jim]

Sounds as if fuel is bleeding back to tank. I'd recommend installing a fuel check valve to stop fuel from going back to tank.

 

[Stubbyie]

I'm uncertain about installing a supplemental check valve. Isn't there one already in the system internal to a pump? It might be that you'd wind up masking the original problem.

On the other hand, if it works, you're ahead--until the original problem gets worse, reappears, and perhaps results in something else failing.

If you do go with a check valve my suggestion would be to use only a spring-loaded check---not the flapper type.

I don't know if these are commonly available (in your area, outside a specialty plumbing wholesaler) in the smallest sizes, but I think you'd be looking for a 1/8-in or 1/4-in spring-loaded check valve in brass with a hose barb screwed into each end (if rubber hoses involved) or flare (not compression, and better if double-lap flare) fittings if steel lines.

Additionally consider adding a supplemental disposable fuel filter immediately ahead of the entry to the spring check valve. These checks are unforgiving of the smallest particles that will keep the valve off its seat and allow undesired backflow.

Please post back your experiences so we may all learn.

 

[North Idaho Wolfman]

Just looked over your fuel system.
You do not have a tractor with a "normal" Kubota fuel system.
Your tractor quite possibly has 2 fuel tanks, one that you can see and fill, and on you can't, It's like an overflow or expansion tank.
I don't know if you have one or not, you'll have to look and verify.
You also have 2 filters, one sediment filter and one water trap filter.
I didn't see any external check valves, and with the piping on your system, I would even consider adding one.
Looks like most of your fuel lines are pressure rated lines, and have bolt on banjo ends, that make it near to impossible to just swap out lines.

When you're done running the tractor, do you shut off the key and it dies or do you have to pull a stop lever?

You said that that the fuel shut off solenoid was replaced, but I can't find a fuel shut off solenoid even listed, But it's possible that it's part of the injection pump, and they don't list those parts separately.

If fuel tanks are flowing as they should (you'll need to verify that by removing lines) then my next thought would be to check seals on filters and operation of the fuel pump.

Fuel piping:

 

[jlputnam1]

Thanks everyone for the suggestions. I very much appreciate your response and time to research the tractor.

I do have the extra fuel tank, which is placed under the battery and radiator. Under the battery is a poor place for a metal tank and mine had rusted to the point that my patching didn't hold any longer, so I bypassed the extra tank several years ago and operated the tractor with the output of the main/upper tank connected to the fuel system where the output of the lower tank was. This configuration worked well for some years before the current starting problem began.

I have replaced the fuel filter and seem to have no flow problems from the tank through the filters, and the output of the fuel pump seems OK as it is able to pump fuel through the system for the bleed process. The starting problems occur even when the main tank is full. With that condition the fuel level in the tank is above all other filter/injector components.

The fuel shutoff solenoid is the single wire version that screws into the lower side of the injector pump body. Turning off the key removes power from the solenoid, which shuts fuel off and stops the tractor. A small click sound is audible when the solenoid is powered or unpowered. A manual safety shutoff is provided near the deck in front of the gear shift lever.

This morning, once again, the tractor didn't start until I completed the bleed procedure and then it needed to crank for about 30 seconds before starting - once running it operated normally. I do seem to get some bubbles at first when bleeding, but can usually get to clear fuel.

I'll try to loosen the fuel cap after shutting the engine off next time, in case it's getting a vacuum in the tank and drawing air into the system as the engine cools.

 

[North Idaho Wolfman]

Where Are you getting the bubbles before the injection pump or after?
If before, leaking diaphragm on the lift pump or pulling air in on a line.
If it after the injection pump to the injectors, is it all of them or just one?
If one or seams like one I would think bad injector.
If it's all of them it still could be a bad injector, but I'm leaning more to needing the injector pump rebuilt.

 

[Daren Todd]

Wolfman,
Does kubota use this style connector for the banjo fitting on the return side of the injection pump

There's a spring loaded ball bearing inside to maintain fuel pressure, and preventing bleed off. Have had a couple get gummed up with fungus, to where they wouldn't seal, have had to tweak a couple of weak springs before too.


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[North Idaho Wolfman]

I don't think they do, all the check valves that I've seen have been external, but Kubota has been know to threw a curve ball in there every now and then!

What is that one on?

 

[Daren Todd]

I don't think they do, all the check valves that I've seen have been external, but Kubota has been know to threw a curve ball in there every now and then!

What is that one on?

Duetz 914, the check valve is actually external, the post that holds the banjo fitting has the check valve built in. I should have backed it out when i took the pic would have made it easier to see. I've come across them on a few other makes as well. Really prevalent on german and italian diesels, but have seen them on some back hoes and dozers as well.

 

[D2Cat]

From your description it sure seems to describe an air leak in a fuel line.

The old Ford 6.9's had a factory water separator that the valve to open and drain would deteriorate and eventually not completely close letting air in. It was tough to find at first because you didn't see any drips, but as it became common knowledge that's the first place one would look, or just replace with a better unit.

Maybe it's a loose clamp, crack in hose or a steel line.

 

[jlputnam1]

Third morning to attempt a start - it's about 65 degrees and I've left the fuel cap loose. I lifted the side panel and manually operated the fuel pump - and got a normal start, maybe turned over twice and idled. Today when I finished work I also loosened the fuel cap and will repeat the process tomorrow morning.

I seem to get bubbles on the first three steps (I do need to pay closer attention to this) - that is the top of the fuel filter, center bolt/banjo fitting, the engine side bleed bolt and the injectors. The final bleed screw on the injector pump seems to not have bubbles in the last step.

I would think that a leak in a line that would let in air would also leak fuel when running and I'm not seeing that.

Thanks again for hanging in with me on this discussion.

 

[Daren Todd]

Third morning to attempt a start - it's about 65 degrees and I've left the fuel cap loose. I lifted the side panel and manually operated the fuel pump - and got a normal start, maybe turned over twice and idled. Today when I finished work I also loosened the fuel cap and will repeat the process tomorrow morning.

I seem to get bubbles on the first three steps (I do need to pay closer attention to this) - that is the top of the fuel filter, center bolt/banjo fitting, the engine side bleed bolt and the injectors. The final bleed screw on the injector pump seems to not have bubbles in the last step.

I would think that a leak in a line that would let in air would also leak fuel when running and I'm not seeing that.

Thanks again for hanging in with me on this discussion.

D2cat is right, it sounds like a pin hole leak in the system. Usually if it's after the fuel pump most of the time it's fairly obvious because of the pressure. Before the fuel pump it's working off a vacume and won't be visible. If it's real bad, you won't be able to prime the system.
Like d2cat said, could be a bad hose, clamp, o'ring or valve in the system. Regular fuel line can get hard and brittle over time. When it get's like that it needs to be replaced. It will start nickle and diming you to death. Loose or stripped out clamps can cause this too. Because it's working on a vacume from tank, if it's just a slight leak around the nipple, it will allow a little air to suck in by the clamp but won't leak or drip do to the pressure from the clamp.

I'll usually use some pieces of clear tubing to rule out issues from the tank to the fuel pump. This will help see where the air is being introduced to the system. This is just temporary. I'll prime the system, and watch real close, and use it to rule out a bad pick up tube, fuel pump, or anything in between. Once i rule out where it's coming from, whether it's a bad fuel pump, pick up tube, or o'ring on a lift screen, i replace the old fuel line with new, and new clamps as well. I stay away from the 1/4 inch wide hose clamps and go with the next size bigger. Have had too many issues with the smaller clamps stripping out or not tightening enough.

Keep us posted on how things turn out